One of the finest American fighter aircraft of World War II, the North American Mustang owed its origin to a Royal Air Force (RAF) specification for a single-seat fighter to replace the Curtiss P-40. The first flight of the prototype NA-73 occurred in October 1940. Production models reached the RAF in November 1941 and these aircraft became known as Mustang Mk I (P-51) and Mk II (P-51A). The original 1,150 hp Allison engine lacked performance at high altitude, and the RAF employed the early Mustangs on low-level armed tactical reconnaissance sorties. Meantime, the US Army Air Force (USAAF) ordered a limited number of P-51s and P-51As as the Apache, to operate in the dive-bomber role.

However, once the basic P-51 design was mated with the proven Rolls-Royce Merlin engine, the aircraft became an enormous success. Through P-51B, C and D models, the Mustang became one of the finest Allied fighters of World War II, and was just as capable at long-range escort as short ground-attack sorties. Fitted with a bubble canopy in place of the earlier 'Razorback' fuselage, the P-51D was the most widely produced version of the Mustang, with 8,956 built.

Interesting developments of the Mustang included the XP-51F and XP-51G lightweight versions and, the fastest Mustang of all, the P-51H, with a top speed of 487 mph at 25,000 ft. The ultimate development of the aircraft occurred post-war, when two Mustang fuselages were joined, resulting in the USAAF's F-82 Twin Mustang.

In November 1944, RAF Mustangs were first flown by the RAAF's No 3 Sqn in Italy.
In 1943, the Australian government arranged for the Commonwealth Aircraft Corporation (CAC) to manufacture the Mustang Mk IV (P-51D) under licence from North American Aviation. The RAAF urgently needed a new fighter, and so the first CAC Mustangs were built mainly from imported semi-finished parts. A prototype Mustang, A68-1001, was used for development trials and the first Australian production Mustang, A68-1, flew on 29 April 1945. This aircraft was handed over to the RAAF on 4 June 1945 and was used for trials by No 1 Aircraft Performance Unit until October 1946. It was placed in storage until 1953 when it was delivered to the Department of Supply at Woomera.

The first 80 Mustang 20s (A68-1/80) were delivered with Packard Merlin V-1650-3 engines, under the CA-17 designation. A second contract called for 170 improved Mustangs, but only 120 were completed. Known as CA-18, the first 40 were built as Mustang 21s (A68-81/120) with Packard Merlin V-1650-7 engines. The remaining CA-18s comprised 14 Mustang 22s (A68-187/200) with Packard Merlin V-1650-7 engines. A CA-21 contract for a further 250 Mustangs was cancelled and, in lieu of the remaining CA-18s and CA-21s, 298 lend-lease P-51Ds and Ks were taken on strength (A68-500/583 and A68-600/813). In addition, the RAAF also accepted Mustangs for the Netherlands East Indies Air Force (N3-600/640).

Produced too late for World War II, RAAF Mustangs were assigned to Japan for occupation duties and, early in 1946, Nos 76, 77 and 82 Squadrons flew into Iwakuni. In 1949 Nos 76 and 82 Squadrons withdrew to Australian and the Mustangs of No 77 Squadron remained to take part in the Korean War from June 1950 until April 1951, when they were replaced by Gloster Meteors.

In Australia, Mustangs remained in service with Citizen's Air Force Squadrons until they were withdrawn from service in 1959.